Electron beam electrical power transmission system

ABSTRACT

Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.

United States Patent [191 Symons 1 1 ELECTRON BEAM ELECTRICAL POWERTRANSMISSION SYSTEM Robert Spencer Symons, Los Altos, Calif.

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: Aug. 20, 1973 [21] Appl. No.: 389,914

[75] Inventor:

3,219,904 11/1965 Osepchuk 321/8 R 3,462,636 8/1969 Seunik et a1. 321/32X 3,479,577 11/1969 Ruden 315/35 X 3,489,943 1/1970 Denholm 328/233 X3,644,778 2/1972 Mihran eta 315/35 3,700,945 10/1972 Friedman.... 315/15Primary Examiner-Saxfield Chatmon, Jr. Attorney, Agent, or Firm-StanleyZ. Cole; D. R. Pressman; H. E. Aire [57] ABSTRACT Electrical power istransmitted from a transmitting lo- CONTRCL CIRCUIT [451 May 27, 1975cation to a remote receiving location by means of an electron beaminjected into an evacuated magnetically shielded pipe extending betweenthe transmitting location and the receiving location. The beam ismagnetically focused within the evacuated pipe. Electrical power to betransmitted is put into the beam in the form of kinetic energy byaccelerating the beam to a high kinetic energy. The kinetic energy isextracted from the beam at the receiving location and converted intopotential electrical energy for application to the load. In oneembodiment, the kinetic energy is extracted from the beam by collectingthe beam current at a potential substantially equal to the potential ofthe source of the electrons, i.e. cathode potential, and causing thecollected beam current to flow through the load to develop the depressedcollector potential. in another embodiment, radio frequency acceleratormeans are utilized for r.f. current density modulating and acceleratingthe beam. The radio frequency current modulation on the beam isextracted at the receiving end by means of radio frequency circuitscoupled to the beam. The extracted radio frequency energy is rectifiedfor application to the load. In another embodiment, AC power atconventional AC power frequencies, as of 60 Hertz, is extracted from thebeam by sequentiallydirecting the beam into a plurality of depressedcollectors coupled to respective primary windings of power transformersfor deriving AC output power for application to a load.

37 Claims, 21 Drawing Figures SHEET MPARATOR MODULATOR FIG. 9

HTEPHEBht-Ifl 27 ms VOLTAGE WAVEFORM (SINE WAVE) CURRENT WAVEFORM SHEETFIG. l3

FIG. l4

FIG. l5

PMENYEQ MY 2 7 1975 2 Vk COMPARATOR COMPARATOR CIRCUIT CiRCUlT SHEETPULSE MOD.

PATENTEU M27 1915 FIG. I? 53 FIG. l8

FIG. l9

L mm T W Cum 0 M 9/ T D 7 W 5 U Q'IJMA Dn 0 LW 5 v 2 9? D DV- V 0 m Mm CH V V ELECTRON BEAM ELECTRICAL POWER TRANSMISSION SYSTEM BACKGROUND OFTHE INVENTION The present invention relates in general to electricalpower transmission systems utilizing an electron beam as the powertransmitting medium and, particularly, to improved means for impartingkinetic energy to an electron beam and for extracting the kinetic energyfrom the beam at a remote location.

DESCRIPTION OF THE PRIOR ART Heretofore, it has been proposed totransmit vast quantities of electrical power from a transmittinglocation to a remote receiving location by means of an electron beamtraveling within an evacuated magnetically shielded pipe or cableemploying strong" magnetic focusing along the pipe to prevent unwantedbeam interception by the walls of the pipe. Such a system is disclosedin U.S. Pat. No. 2,953,750 issued Sept. 20, i960.

In this prior proposed scheme, it was contemplated that kinetic energywould be imparted to the beam at the sending end by accelerating thebeam to a high ki netic energy, as of 100 MeV, by a modified betatrontype induction accelerator machine. In the modified betatron, the beam,while magnetically contained within a helical magnetic cable (pipe), wascaused to pass through a plurality of accelerating gaps for increasingthe kinetic energy of the beam in a steplike fashion. That is, theaccelerating electrical field, produced across the respective gaps by anAC potential applied in synchronism with pulses of the beam, caused thebeam to be accelerated to the high output kinetic energy. It wascontemplated that the high energy pulses of beam current could be at ACpower frequencies of 25 or 60 Hertz or, as an alternative, the pulserepetition rate could be in the radio frequency range by utilizing aradio frequency cavity resonator at each of the accelerating gaps in thehelical cable.

The kinetic energy of the high energy pulses of beam current wasextracted at the receiving end by means of a reverse type acceleratorwhich decelerated the beam pulses in accordance with the amount of powerdemanded by the load. The decelerated (unused) pulses of beam currentwere returned to the sending end by means of return magnetic cables orpipes connected back to appropriate ones of the electron beamaccelerating machines. The returning beam pulses were 180 out of phasewith the transmitted pulses of beam cur rent leaving the machine. Inthis manner the unused energy of the beam was returned to the betatronaccelerating machine.

It was concluded, in the above cited prior patent, that the radiofrequency alternative was not feasible for transmitting relatively largeamounts of power. On the other hand a problem with the use of magneticinduction accelerators operating even at conventional power frequenciesis that a vast amount of iron must be used causing attendant iron lossesdue to hysteresis effects.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of an improved electrical power transmissionsystem employing an electron beam as the power transmission medium.

In one feature of the present invention, kinetic energy is imparted tothe beam at the transmitting end of the power transmission system and isextracted from the beam at the receiving end by decelerating andcollecting the electrons of the beam at nearly zero velocity, wherebythe kinetic energy of the beam is efficiently converted to electricalpotential energy.

In another feature of the present invention, a magnet beam focusstructure, of either the permanent magnet or electromagnet type, isdisposed surrounding the vacuum envelope containing the beam, and thebeam focus magnets are surrounded by a magnetic shield, whereby themagnet structure is disposed outside of the vacuum envelope containingthe beam such as to minimize outgassing problems and contamination ofthe vacuum containing the beam.

In another feature of the present invention, a magnetic beam focusingtransition section is provided at the power transmission location forgradually increasing the intensity of the beam focus magnetic fields inthe direction of electron flow from the cathode emitter to minimizeundesired perturbation of the electron beam.

In another feature of the present invention, the magnetic beam focusstructure includes a beam entrance transition section having anastigmatic plural pole magnetic lens for providing a smooth transitionof the electron flow into the main portion of the beam focus structure,to avoid undesired pertubation of the electron beam flow.

In another feature of the present invention, beam current collected atthe receiving location is returned to the transmitting location via thepipe containing the beam, whereby the return current path is symmetricalrelative to the beam path to prevent magnetic defocusing of the beam.

In another feature of the present invention, a DC beam acceleratingstructure is employed at the transmitting end, such D.C. beamaccelerating structure comprising a sequence of beam acceleratingelectrodes operating at sequentially higher beam accelerating potentialssuch as to produce a DC beam accelerating field in the beam path foraccelerating the beam to a high energy, whereby a relatively simple,inexpensive and efficient beam accelerator is obtained.

In another feature of the present invention, a DC. beam deceleratorstructure is provided at the receiving end of the electrical powertransmission system, whereby the high kinetic energy electron beam iscaused to pass through a series of beam decelerating electrodessequentially operated at lower potentials for decelerating the beamwithout intercepting a substantial percentage of the high velocityelectrons on the decelerating structure. The kinetic energy of the beamis thereby efficiently converted into DC. potential energy.

In another feature of the present invention, kinetic energy is impartedto the beam at the transmitting end by passing the beam through a radiofrequency accelerator. Radio frequency wave energy is extracted from thebeam at the receiving end or tapped off in interm ediate locations bymeans of a receiving radio frequency wave supportive structure excitedby the RF energy imparted to the beam at the transmitting end.Rectifiers are coupled to the receiving radio frequency structure forconverting the radio frequency energy to DC. power for application tothe load.

In another feature of the present invention, radio frequency resonatorsare periodically spaced along the beam path intermediate thetransmitting and receiving ends for rebunching the beam to counteractspace charge debunching effects.

In another feature of the present invention, a control circuit isprovided for monitoring the power demanded by the load at the receivingend of the transmission sys' tem and for causing the power transmittedto be equal to the power demanded at the receiving end.

In another feature of the present invention, the beam power transmittedfrom the transmitter end to the receiver end is pulsed into a train ofpulses, each having a duration shorter than the time required to formsufficient ions to fully neutralize the beam space charge, withsuccessive pulses being separated by a short time for ion drainageduring which time positive ions are drained to the walls of theenvelope.

In another feature of the present invention, ion draining electrodes aredisposed along the beam path for collecting and draining positive ions.

In another feature of the present invention, a plurality of beamcollector structures are provided at the receiving end of thetransmission system and a beam deflector is provided for sequentiallydeflecting the beam into respective ones of the beam collectorstructures for supplying alternating current to the load.

In another feature of the present invention, a plurality of electronguns are energized with alternating beam voltage at the transmitting endof the power transmission system and a beam deflector is provided at thetransmitting end for sequentially directing the current from respectiveones of the electron guns into a common beam path leading to thereceiving end, whereby A.C. power at the transmitting end is efficientlyrectitied into direct beam power for transmission to the receiving end.

In another feature of the present invention the beam current ispulse-modulated for control of the average electrical power transmittedto the receiving location.

In another feature of the present invention, radio frequency load meansare coupled in RF wave energy exchanging relation with the interior ofthe evacuated beam pipe for coupling to and suppressing undesired modesof wave energy propagation within the pipe.

In another feature of the present invention the period of a periodicbeam focus magnet structure is varied randomly to avoid undesiredcumulative radio frequency wave-beam interactions, whereby undesiredoscillations are avoided.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification taken inconnection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic longitudinalsectional foreshortened view, partly in block diagram form, of anelectron beam power transmission system incorporating features of thepresent invention,

FIG. IA is a sectional view of the structure of FIG. 1 taken along linelA iA in the direction of the arrows,

FIG. 2 is an enlarged sectional view of a portion of the structure ofFIG. I taken along line 2-2 in the direction of the arrows,

FIG. 2A is a view similar to that of FIG. 2 showing an alternativeembodiment of the present invention,

FIG. 3 is an enlarged schematic detail view of a portion of thestructure of FIG. I delineated by line 3-3,

FIG. 4 is a schematic longitudinal sectional view of a portion of FIG. Idelineated by line 4-4,

FIG. 5 is a view similar to that of FIG. I depicting an alternativeembodiment of the present invention,

FIG. 6 is a schematic circuit diagram of the winding portion of thetransformers of the circuit of FIG. 5 de lineated by line 6-6,

FIG. 7 is a schematic circuit diagram of the winding portions of thetransformers of FIG. 5 delineated by lines 7-7,

FIG. 8 is a transverse sectional view of a portion of the structure ofFIG. 5 taken along line 8-8 in the direction of the arrows,

FIG. 9 is a schematic diagram, partly in block diagram form, of anelectron beam power transmission system incorporating alternativeembodiments of the present invention,

FIG. 10 are waveforms of beam voltage, beam cur rent, and grid voltagefor an electron beam power transmission system employing an interruptedbeam,

FIG. 11 is a schematic line diagram of an electron beam powertransmission system employing alternative features of the presentinvention,

FIG. I2 is a schematic line diagram ofa power transmission systememploying alternative embodiments of the present invention,

FIG. 13 is a schematic line diagram of an alternative embodiment to aportion of the structure of FIG. 11 delineated by line 13l3,

FIG. 14 is a schematic circuit diagram for an electrical powertransmission system incorporating features of the present invention anddepicting an alternative embodiment,

FIG. 15 is a plot ofcurrent and voltage waveforms for one phase of thepower transmission system of FIG. 14,

FIG. 16 is a view similar to that of FIG. 1 depicting an alternativeembodiment of the present invention,

FIG. 17 is a schematic circuit diagrm, partly in block diagram form, ofa control circuit useful in a power transmission system of the presentinvention,

FIG. 18 is a view similar to that of FIG. 17 depicting an alternativeembodiment of the present invention, and

FIG. 19 is a schematic circuit diagram, in block form, of the comparatorcircuit useful in the embodiment of FIGS. 17 and 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show an electronbeam power transmission system 11 incorporating features of the presentinvention. System 11 includes an electron gun l2 and a DC beamaccelerator section 13 at the power transmitting end 14 of an elongatedevacuated envelope 15 which extends for a substantial distance, e.g. 0.Ito 1,000 miles, to a remote power receiving location 16 at the receivingend of the transmission system I. At the receiving location 16, anelectron beam collector structure 17 is connected to the evacuatedenvelope I5 by a DC beam decelerating section 18.

Briefly, electron gun 12 serves to form, accelerate and project a beamof electrons 19 into the beam accel erator section 13 which acceleratesthe beam to a very high energy, as of in excess of 0.1 million electronvolts MeV, and preferably in excess of 0.5 MeV. In this manner,substantial kinetic energy is imparted to the electron beam.

Although a separate accelerator section 13 is employed in the embodimentin FIG. 1, this is not a requirement. If the beam voltage is below 0.25MeV, the anode of the gun 12 may be operated at 0.25 MeV foraccelerating the beam up to 0.25 MeV. Actually the accelerating section13 can be considered as part of the anode structure of the gun 12.

The beam 19 is then projected axially into the elongated envelope 15.The beam is magnetically confined in envelope 15 by a quadrupolemagnetic beam focus structure 22 to avoid substantial interception onthe walls of the evacuated envelope. An astigmatic magnetic lens system21 (See FIGS. 1 and 1A) is provided between the accelerating section 13and the entrance to the elongated envelope [5 to provide a smoothmagnetic focusing transition of the electron stream from the acceleratorinto the quadrupole beam focus field in envelope 15.

The magnetic lens system 21 comprises one or more guadrupole lenses.Each quadrupole lens includes four magnetic poles of alternatingpolarity around the envelope 15 which are energized by electric coilswound around the poles 9. A tubular magnetic shield 20 surrounds thepoles 9.

The quadrupole magnetic beam focus structure 22, more fully describedbelow, spirals around envelope to provide strong" magnetic beam focusingof the type described in the aforecited U.S. Pat. No. 2,953,750. Theenvelope 15 is evacuated by means of a plurality of glow dischargegetter-ion vacuum pumps 23 or any other suitable vacuum pump disposed atsuitable intervals along the pipe 15 in gas communication therewith forevacuating same to a relatively low pressure as of 10 torr. Thus a beamcan be transmitted for hundreds of miles through tubular envelope 15without substantial loss of energy.

As an alternative to the use of the quadrupole lens 21, the quadrupolebeam focus structure 22 is extended into a transition region between thecathode 31 of the gun l2 and the entrance to pipe 15. In this transitionregion, the quadrupole beam focus magnetic field intensity in the beampath gradually increases in strength from zero to its full value at theentrance to the main portion of the pipe 15 (see FIG. 13),

At the power receiving location 16, the beam is decelerated by a beamdecelerator section 18 to a potential as close as possible to thepotential of the source of electrons within the gun 12, therebyconverting the kinetic energy in the beam to potential electricalenergy. The electrons of the beam, having low velocity (i.e. within 5%of the collector potential), are collected on the interior walls of thebeam collector structure 17, which operates close to the potential ofthe source of electrons within the gun 12, whereby the beam energyconverted to heat in beam collector 17 is minimized.

The collected beam current is caused to flow through an inverter load 24to the vacuum envelope 15, typically at local ground potential. Thecollected beam current is returned to the transmitting location 14 viathe electrically conductive walls of the envelope 15. The inverter 24inverts the DC power to three phase AC output power which is supplied onoutput lines 25, 26 and 27. In a typical example, the beam 19 has acurrent of 1,000 amps and is accelerated by the accelerator section 13to a potential of one million volts, such that the power transmitted bythe beam from transmitting location 14 to receiving location 16 is lgigawatt.

A control circuit 28, as more fully disclosed below with regard to FIGS.17-19, monitors the potential V of the beam collector 17 and compares itwith the potential V of the source of electrons to derive an errorsignal for controlling the beam current via a control electrode 29 inthe electron gun 12 or adjustment of V such that the power transmittedto the receiving end 16 is regulated to match the demand for power atthe receiving end 16.

The electron gun 12 includes a spherically concave thermionic cathodeemitter 31 of sufiicient area to emit the required electron current,such as L000 amps. Cathode emitter 31 is heated to thermionic emissiontemperature by means of a filamentary heater 32. Operating power issupplied to the filamentary heater 32 from a power supply 33. A focuselectrode 34 surrounds the peripheral edge of cathode emitter 31 to aidin shaping the electron beam in the region of cathode emitter 31.

The control grid 29 is preferably of the type protected by a shadow gridwherein the shadow grid structure, operating at substantially cathodepotential, is disposed immediately adjacent the surface of the cathodeemitter 31 and the control grid has apertures aligned with the aperturesin the shadow grid. As an alternative to a control grid, a modulatinganode may be employed as the control electrode 29.

The cathode emitter 31 is preferably dimpled, with the dimples having alesser radius of curvature than that of the composite cathode emittersurface. The individual dimples in the cathode serve as separate cathodeemitters for individual electron beamlets passing through the alignedopenings in the shadow and control grid structures in a substantiallynon-intercepting manner. Such an electron gun and control grid structureis disclosed and claimed in U.S. Pat. No. 3,558,967, issued January 26,1971, and assigned to same assignee as the present invention.

In a typical example, thermionic cathode emitter 31 comprises animpregnated tungsten matrix cathode approximately 15 cm. in diameter andhavng an area of approximately 350 cm At 1,000 amperes, such a cathodewould operate at a current density of approximately 3 amperes per squarecentimeter. Tunsten matrix cathodes, impregnated with barium aluminate,can operate continuously for five years at this current density.

The beam accelerator section 13 is preferably of the type used with theVan de Graaff or Cockroft-Walton generators and is disclosed in anarticle entitled Electrostatic Generators for the Acceleration ofCharged Particles appearing in Reports on Progress in Physics, Vol.ll:l-l8 (l948). Briefly, this type of accelerator includes a sequence ofgenerally planar centrally aper tured plate shaped electrodes 35 whereinthe accelerating potential, as of 0.1 to 5 million volts, is evenlydistributed among a number of the accelerating electrodes 35. Apotential divider 36 employs a string of resistors to divide the beampotential V,, for application of respectively increasing potentials tothe respective ones of the accelerating electrodes 35. The potentialdifference between successive electrodes 35 in the accelerator section13 is preferably less than 200 kilovolts to prevent arcing between theadjacent electrodes 35.

Electrodes 35 serve to provide a uniform beam accelerating electricfield within the beam path 19; the first few ones ofelectrodes 35 nearthe upstream end of the beam path 19 serve to focus and to converge theelectron stream. In a typical example, the beam would be converted froma diameter of l cm. at cathode emitter 31 to approximately a diameter ofS cm. at the output end of accelerator section 13.

A three phase rectifier 38 receives the three phase input power from apower generator or the like and rectifies this three phase input toproduce direct output current at a high negative cathode voltage V as of0.l million volts to 5 million volts.

FIG. 2 shows, in section, the evacuated envelope 1S and beam focusstructure 22. More particularly, evacuated envelope 15 comprises a pipemade of an electrically conductive material, as of aluminum. In apreferred embodiment, the pipe also serves as the return electricalconductor of the power transmission system I such that the collectedbeam current flows back to the power supply of the electron gun 12through a return path which is symmetrical relative to the beam 19. Inthis manner, undesired magnetic defocusing of the beam by the magneticfield of the beam current loop is avoided. ln the preferred embodiment,the pipe 15 is electrically insulated from earth such as by the ferritepermanent magnets 22. In a typical example, aluminum pipe 15 has adiameter of approximately cm. and a wall thickness of approximately 3mm.

The beam focus permanent magnets 22 are disposed around pipe at 90spacing for a quadrupole type of strong magnetic focusing. In strongmagnetic beam focusing a quadruple magnetic field is provided which hasflux lines which lie in planes almost perpendicular to the direction ofthe beam. The flux lines are made to rotate about the beam by spiralingpermanent magnets 22 around pipe 15. The permanent magnets are radiallypolarized, with the magnetic poles alternating in polarity in thecircumferential direction around the pipe 15. Although the preferredembodiment utilizes a quadrupole magnetic structure, other multiple polestructures may also be used, such as 6, 8, 10 or l2 poles etc. Alsoother types of magnetic focusing may be employed such as a series ofdiscrete magnetic lenses or a confining magnetic field.

As an alternative to the use of permanent magnets for producing the beamfocus magnetic field, electromagnets are employed. The electromagneticequivalent is useful where operating temperatures are encountered whichare outside of the rated operating temperature range of the permanentmagnet material. A quadrupole electromagnetic beam focus structurecomprises four conductors 40 spiraling around the pipe 15 in 90 circumferentially spaced relation (see FIG. 2A), and energized with directcurrent of opposite direction in adjacent conductors 40.

An electron traveling parallel to the beam path 19 will interact with amagnetic vector at right angles to its direction of travel. The fieldhas a strength proportional to the distance between the electron and theaxis of the beam path. The magnetic vector rotates in a direction aroundthe pipe at twice the rate of the quadrupole rotation. The magneticvector will cause the electrons to follow helical paths. The magneticfocusing force of the quadrupole field on the electron, when theelectron is far from the axis, is larger than the defocusing force whenthe electron is near the axis. As a result, there is a net time averagedinward focusing force.

In this kind of focusing, the magnetic field need only provide afocusing force that is sufficient to compensate for the differencebetween the space charge forces, which tend to defocus the beam, and thebeam self focusing magnetic field. The problem of focusing the beam isless severe at high beam voltage since the space charge forces arereduced at a given current flow and the self magnetic field of the beamtends to compensate the space charge repulsion. This means that smallerfo cusing fields can be used to confine the beam. For example, at onemillion volts, 8/9 of the space charge force is neutralized by theself-magnetic field of the beam current. Since the focusing force isproportional to the distance of the electron from the axis of the pipe15, the beam will tend to follow the center of pipe 15 even if the pipehas curvature.

Magnetic focusing results in ion trapping, which leads to plasmainstability. Residual gas molecules within the pipe, when struck byelectrons produce positive ions which are attracted toward the center ofthe beam. The positive ions in the center of the beam tend to neutralizethe space charge repulsion, causing the beam to condense toward thecenter. Therefore, ion drainage or neutralization is required. Thesimplest way to obtain ion neutralization is to turn off the beamperiodically for a few microseconds to allow the ions to move to thewall of the pipe 15, where their change will be lost. The time requiredfor ion neutralization of the beam at a pressure of 10'' torr at anelectron energy of l megavolt is about 5 milliseconds. Thus, the beam isturned off by means of grid 29 every few hundred microseconds, for a fewmicroseconds, causing any ions that have formed to mutually repel eachother and drain to the wall. As an alternative, (shown in FIG. 3)insulated negative electrodes may be provided at suit able spacingsalong and within the pipe 15 for generation of periodic electric fields(potential) wells) for drawing the ions to the electrodes. Moreparticularly, each ion drain may include an enlarged diameter section ofthe pipe 15" to provide an annular recess to receive a metallic ringshaped drain electrode 1 supported from a conductive post 2 via afeedthrough insulator 3. The post 2 is connected to source of negativepotential 4, as ofto l ,000 V, for collecting and draining positive ionsfrom within the pipe 15. Various suitable ion draining electrodes andschemes are disclosed in US. Pat. No. 2,963,605 issued Dec. 6, 1970.

In a preferred embodiment, the permanent magnets 22 are made of grainoriented ferrite particles with a BH product of nearly 4 milliongauss-oersteds. Such a material is commercially available at 2,000 gaussand 2,000 oersteds in which the ferrite particles are bonded in aflexible plastic so that half of the energy product of the orientedferrite is sacrificed for the convenience of flexible plastic bonding.Such a material has sufficient magnetic energy for this application.This material is also relatively inexpensive in large quantity. Anyother permanent magnetic material might be substituted.

For a permanent magnet focus system capable of focusing, for example, aone megavole, one thousand ampere beam, the energy stored in thefocusing field is 0.69 joule per meter of length; therefore, 16,000cubic inches of one million gauss-oersted magnetic material per mile ofline length would be required. The magnets 22 are placed external to thevacuum envelope 15 so as not to contaminate the vacuum. A tubularmagnetic shield 41 surrounds magnets 22. In a typical example, themagnetic shield 41 may comprise a spiral wound soft iron tape 0.010 inchthick. The focusing magnetic field required inside of the pipe 15 forfocusing the beam is in the range of I to 200 gauss.

The vacuum envelope 15 is evacuated by a plurality of glow dischargegetter ion vacuum pumps, such a VacIon pumps commercially available fromVarian Associates of Palo Alto, Cal. These pumps have no moving parts,produce extremely clean vacuums free from any oil contamination andconsume very small amounts of power when pumping on a closed system. Inaddition, these pumps have very long life under these conditions.Approximately 18 8-liter per second vacuum pumps 23 are required foreach mile of length of the pipe 15. Such a vacuum system would consumeapproximately 0.54 watt per mile (3,000 volts at 180 microamperes).

Under certain operating values of beam voltage and current and as afunction of the diameter and length of the pipe 15, microwaveelectromagnetic interaction may be obtained between space charge wavesof the beam 19 and microwave energy propagating within the pipe 15. Thisresults in undesired velocity and current modulation of the beam as wellas the generation of undesired amounts of microwave energy within thepipe 15. Accordingly (See FIG. 4), wave traps 5 or other means ofcoupling a lossy material to the microwave electromagnetic fields withinthe pipe are located along the pipe for absorbing the undesiredmicrowave energy to damp out undesired microwave oscillations. In atypical mode trap 5, an evacuated chamber 6 containing an array ofresistive card wave energy absorbers 7 is coupled to the microwavefields of the pipe 15 via a suitable coupling slot or hole 8. As analternative, the inside wall of the pipe 15 may be coated with a lossycoating of a lossy alloy of Al, Fe and Co, such as Kanthal.

As another alternative, the pitch of the spiraling quadrupole beam focusmagnet structure is varied by, for example, i percent in a random way toavoid cumulative fast wave beam-field interactions and their resultingoscillations.

At the receiving location 16 the beam decelerating section 18, similarto the beam accelerator section 13 except turned end-for-end, serves todecelerate the beam to a beam voltage as close as possible to thevoltage of the cathode emitter 31, namely, V without reflecting beamcurrent to the decelerator section 18.

The decelerated beam is received within the depressed beam collectorstructure 1'7; the collector operates at a potential V approximatelyequal to the decelerated beam or source potential V;,. In a preferredembodiment, the depressed collector structure 17 is of the typedisclosed and claimed in US. Pat. No. 3,453,482 issued July l, 1969 andpreferably includes the improvement of the center spike as disclosed andclaimed in copending US. patent application Ser. No. 283,433 filed Aug.24, 1972. both assigned to the same assignee as the present invention.The depressed collectors of this type are very efficient and operatewith beam collecting efficiencies of 98 percent, i.e., only 2 percent ofthe transmitted power is lost in the collector 17. However, in a onegigawatt transmission system with 98 percent beam recovery, there isstill 20 megawatts of power which must be dissipated in the collector17.

The collector 17 is preferably of the water or liquid cooled typedisclosed in US. Pat. Nos. 3,374,523 issued Mar. 26, 1968 and 3,414,757issued Dec. 3, 1968 and assigned to the same assignee as the presentinvention. The collector should be scaled in size such that the powerdissipation on the interior surfaces thereof results in a power densityof below one kilowatt per square centimeter.

One main advantage of the electrical power transmission system 11 of thepresent invention is that it provides means for transmitting a gigawattquantity of electrical power at relatively low cost per mile and lowloss. This is because of the elimination of high voltage, the source ofmost of the problems is conventional transmission lines, from the mainportion of the line. Energy is transmitted instead in kinetic form bymeans of a beam of electrons. The high energy electron beam is launched,transmitted through evacuated pipe 15 and recovered with losses lowenough to be competitive with conventional overhead high voltagetransmission lines. The economic savings in right-of-way cost andecological advantages of less ozone generation and elimination ofunsightly towers or excavations in either underground or above groundinstallations justify its use. Pipe 15 may be installed underground in aditch or, for above ground systems, can simply lie on the surface or besupported by bents, a catenary, or existing bridge structures.

FIGS. 5-8 show a polyphase electric power transmis sion system 42similar to that previously described with regard to FIGS. 1-2 with theexception that the rectification and inversion functions have beencombined with the transmission system. More particularly, six separateelectron guns 12 and their respective beam accelerator sections 13 aredisposed at the transmitting location 14 for projecting six separateelectron beams into respective pipes 15'. Each pipe is magneticallyshielded and provides strong magnetic focusing and converges toward thecommon magnetically shielded and magnetic focused pipe 15 leading to thereceiving location 16. A magnetic deflection yoke 43 is provided at theconfluence of the respective beam input pipes 15, at the transmittinglocation 14, for sequentially and selectively deflecting the electronbeams from respective ones of the electron guns 12 into common pipe 15.

Similarly, at the receiving location 16 the main transmission pipe 15splits into six separate pipes 15' each leading to a respective beamdecelerator section 18 and a depressed collector 17. A magneticdeflection yoke 44 is provided for sequentially deflecting the outputelectron beam into respective ones of the output pipes 15'. Deflectionyokes 43 and 44 are of the conventional type used in cathode-ray tubesor in accelerator-totarget deflection systems of high energy particleaccelcrating machines such as at the Stanford Linear Accelerator Centerat Stanford, Cal.

Input power to be transmitted to the receiving location 16 is suppliedto the transmitting location 14 from a suitable generator, not shown.The three phase input power is applied to the primary windings 45 of aninput transformer 46. The primary windings 45 are connected in the deltaconfiguration as shown in FIG. 6 and the secondary windings 47 of theinput transformer 46, as shown in FIG. 7, are each center-tapped atground or V potential and wound in a 6 phase configuration. The oppositeends of the center-tapped windings 47 are coupled to the cathodeemitters of each of the pair of guns 12 for a respective phase of thethree phase transmission system. For example, for the A phase, one endof the cententapped winding 47 is coupled to one gun and the other endof the center-tapped winding 47 is coupled to the other gun. Due to theself rectification characteristic of the thermionic diodes, each of theguns ofa particular phase would, in the absence of a control electrode29, conduct only during one-half of the cycle, such conduction halvesbeing 180 out of phase with respect to each other.

Control signals are applied to the control grids 29 via modulators 48for limiting the beam conduction phase angle for each gun 12. Moreparticularly, the conduction phase angle is limited to a firstapproximation to 3o0l2p where p is the number of phases for thepolyphase transmission system 42. In the case of a three phase systemutilizing six electron guns, the beam conduction angle for each of theguns is limited to 60, and would normally be centered on the time whenthe applied voltage is a maximum. The operation of the magneticdeflection yoke 43 is synchronized with the potentials applied to eachof the respective guns via leads 49 which feed into a deflection controlcircuit 51 and which serve to synchronize the input and output beamdeflectors 43 and 44, respectively. such that the beam current isdirected into the proper beam collector 17.

At the power receiving location 16, each phase of the three phase systemhas its respective pair of collectors connected to opposite ends of oneof three center tapped primary windings 52 of an output transformer 53.The secondary windings 54 of the output transformer 53 are connected inthe delta configuration as shown in FIG. 6. An output voltage Vc issensed across each of the respective phases of the output primarywindings 52 via voltage sensors 55 (See FIG. 9) and these voltages arefed back to the gun modulators 48 to control the amount of the beamcurrent drawn from each of the respective guns such that the powerdelivered to the load is equal to the power demanded by the load as morefully described below with regard to FIGS. 17l9.

Due to the relatively short conduction phase angle for each of theelectron guns and therefore the short phase angle for current deliveredto each of the respective collectors, the current pulses delivered tothe primary windings 52 of the output transformer 53 will be rich inharmonics of the power frequency.

However, the connection of the collectors 17 of each phase (three phasesystem) to opposite ends of each of the respective output primarywindings 52 serves to cancel out the even harmonics of the powerfrequency (i.e. 60 Hz). In addition. the balanced connection of thecollectors 17 relative to the centertap in the output primary windings52 serves to prevent undesired saturation effects of the transformer 53due to the DC component of current flowing through each primary winding52. The third harmonic and multiples thereof are effectively cancelledby using the delta connected secondary windings. The fifth, seventh,eleventh, thirteenth, etc. odd harmonics are bypassed by means ofmultiplicity of series resonant filters, such as filter 56, tuned foreach respective odd harmonic and connected in shunt with the respectiveprimary output winding 52.

The delta winding connection for cancelling of the third harmonic andmultiples thereof is only operative in a three phase system or multiplesof a three phase system. Accordingly, in a single phase or two phasesystem series resonant bypass filters 56 are employed for each thirdharmonic or odd multiples thereof, such as 3rd, 9th, l5th, etc.

Typically, the lowest harmonic will have the largest amplitude. Thus, afifth harmonic filter 56 may suffice dependent upon the shape of thebeam current pulse. Also the beam current pulse is preferably shaped bya waveform shaping circuit which shapes the control electrode potentialto reduce the 5th, 7th, llth. 13th. etc. harmonics of beam current. Sucha wave shaping circuit is contained within modulator circuit 48 and isoperative upon the shape of the signal fed to control electrode 29.

For example, for a beam current pulse train as shown in FIG. 10, thereis a certain value of beam conduction angle which will reduce any givenharmonic of the pulse repetition frequency of beam current to zero.Thus, the wave shaping circuit controls the beam conduction angle tominimize the certain harmonic.

Each of the primary bindings 52 has a bypass capacitor 57 connected inparallel with the inductance of each of the primary windings 52 forbypassing harmonics of higher order than those filtered by filters 56.

Referring now to FIG. 9, there is shown an alternative electron beampower transmission system similar to that previously described withregard to FIG. 5 with the exception that a pair of magnetically shieldedand magnetically focused pipes 15 are employed for each phase of the ACpower transmission system. For example, in a single phase system twopipes 15 are employed. The pair of electron guns 12 for each phase ofthe AC power transmission system are connected in out of phase relationby connection of the cathode emitters 31 to opposite ends of a centertapped secondary winding 47 of the input transformer 46.

The advantage of the AC power transmission system of FIG. 9 is that theconduction phase angle can be increased to a value substantially inexcess of the 60 conduction phase angle for the three phase system ofFIG. 5. This reduces the harmonic content in the beam current suppliedto the output transformer 53.

However, it is generally undesirable to employ the whole 180 beamconduction phase angle during each conductive half cycle of the appliedalternating beam potential. The reason for this is that at relativelylow values of beam voltage V,,, the electrons have relatively lowvelocities and thus corresponding relatively long transit times throughthe pipe 15. In such a case, some overtaking of the slow electrons maybe obtained by subsequent fast electrons. This has a deleterious effectupon the beam collector efficiency since, for high collector efficiency,all the electrons at a given instant in time should have the samevelocity. Also, such overtaking will cause distortion of the currentwaveform, usually increasing the unwanted harmonic content thereof.Also, the beam focus system, depending upon the particular magneticfocusing scheme employed, may not properly focus electrons over wideranges of electron velocities.

Therefore, it is preferred to limit the conduction of beam current toonly a portion of the cycle of applied beam voltage corresponding to avalue of beam current greater than one-sixth of the peak or maximum beamcurrent, ie. I /G.

Referring now to FIG. 10, there is shown the waveforms for beam currentI,,, beam voltage V,, and control electrode voltage V and V The beamconduction angle is readily controlled by applying a fixed DC negativebias voltage V to each of the respective control electrodes 29 such thatthe beam conduction angle is limited to that portion of the cyclecorresponding to a respective grid voltage exceeding the cathode voltageV;,. The beam conduction angle can then be varied and controlled asdesired by increasing or decreasing the magnitude of the dc negativegrid bias voltage V Returning again to FIG. 9, it is desirable tocontrol the power factor of the load as reflected into each of theprimary windings 52 of the output transformer 53 such that the collectedbeam current I is in phase with the respective collector potential VAccordingly, a continuously variable reactance, such as that provided bya synchronous condenser 58, is preferably connected across each of therespective output delta connected secondary windings 54. A voltage isderived which is proportional to the collected beam current I Thisvoltage is derived from a current transformer 59 connected between thecentertap of the primary winding 52 and the pipe 15. This voltage is fedto one input of a phase comparator 60 for comparison with the phase ofthe respective collector voltage V as derived from sensor 55 to derivean error output which is fed to the field control of the synchronouscondenser 58 for causing the condenser 58 to take the proper value ofreactance to bring the beam collector current I into phase with thecollector voltage V The power factor control circuitry of FIG. 9 is alsoutilized to advantage in the system of FIG. 5.

Referring now to FIG. 11, there is shown an AC power transmission systemsimilar to that of FIG. 9 wherein a common magnetically focused andmagnetically shielded pipe is employed for each phase of the AC powertransmission system. More particularly, con vergent and divergent pipes15', as previously described with regard to FIG. 5, are employed at thetransmitting and receiving locations, respectively, for feeding theelectron beams from the guns of each phase into the common pipe 15 andout of the common pipe to respective collectors of each phase. Thedeflection of the beams at the transmitting and receiving locations isobtained by a deflection control circuit driving each of the deflectingmagnets 43 and 44 in response to inputs derived from the respectiveguns. The advantage of the sytstem of FIG. 11 over that previouslydescribed with regard to FIG. 9 is that only one pipe 15 is required foreach phase of the AC power transmission system.

Referring now to FIG. 13, there is shown an alternative embodiment tothat portion of the structure of FIG. 11 delineated by line 13-13. Moreparticularly, the input deflection magnet 43 is replaced by strongmagnetically focused and convergent input pipes 15". However, magneticdeflection is still required at the receiving location.

Referring now to FIG. 12, there is shown an alterna tive three phasepower transmission system 59 incorporating alternative embodiments ofthe present invention. More particularly, the system is similar to thatpreviously described with regard to FIG. 9 with the exception that onlyone pipe 15 is provided for each phase of a three phase system andcollection of beam current through each phase of the three phase systemoccurs only once per cycle at the power frequency as contrasted withtwice per cycle at the power frequency as indicated in FIG, 10. Thewindings 47 and 52 have only three phases as contrasted with six phasesas shown in FIG. 7.

The power transmission system 59 of FIG, I2 has the advantage ofsimplicity in that it provides only one pipe 15 per phase of the threephase system but it has the disadvantage that the harmonic content ofthe current delivered to the primary windings 52 of the outputtransformer is greater than that obtained in the system of FIG. 9.

Referring now to FIGS. 14 and I5, there is shown an alternative multiplepipe polyphase A.C. transmission system 62. Transmission system 62 issimilar to that of FIG. 5 with the exception that a pair of pipes 15 ispro vided for each phase of the polyphase system, as shown in the systemof FIG. 9. In this system 62, the beam current through each of the pipes15 does not have to be limited to 360/2p of phase angle where p is thenumber of phases. In the case ofa three phase system, the conduction ofcurrent is preferably iimited to a phase angle such that the currentconducted has a value greater than 1/6 lmax, where lmax is the peak beamcurrent for each phase. This means that current is conducted from eachgun for approximately l20l40 of phase angle of the input voltagewaveform, as shown in FIG. 10. This reduces the harmonic content in thecurrent flowing in the primary windings 52 of the output transformer 53.One advantage of the system of FIG. 14 is that the filtering ofundesired harmonics in the output of the transformer 53 is simplified atthe expense of ad ditional pipes 15. A second advantage is the elimination of the magnetic deflectors 43 and 44.

A further advantage of the system of FIG. 14 is that the beam currentreturn paths are separate for each beam to prevent cross flow of beamreturn current flow with attendant potential differences between thevarious pipes 15 as encountered with unbalanced loads. However, thewindings 47 and 52 are balanced in the transformers 46 and 53 to avoidDC. saturation of the transformer cores, i.e., bucking connected forbeam current flow.

As an alternative to the system 62 of FIG. 14, the number of pipes 15can be reduced to one per phase of the polyphase AC. system by using acommon pipe IS per phase and employing the magnetic deflection system ofFIG. 11 for sequentially deflecting beams from respective pairs of guns12 into and out of the respective common pipe 15. In this latter system,the input magnetic deflection can be eliminated since the input magneticpipes 15' will focus the respective beams sufflciently to allow theindividual beams to negotiate the bends in the pipes 15 at theconfluence of the pipes 15 with the common pipe 15 as shown in FIG. 13.

Referring now to FIG. 16, there is shown an alternative transmissionsystem 72 of the present invention. The power transmission system 72 ofFIG. 16 is similar to that of the system of FIG, 1 with the exceptionthat RF accelerator means 73 are employed for bunching and acceleratingthe beam to relatively high energies, for example, MeV.

The radio frequency accelerator 73 comprises a plurality of individualcavity resonators 74, as of 250 such cavities, sequentially arrangedalong the beam path 19 for successive electromagnetic interaction withthe beam for velocity modulating the beam with RF energy at the resonantfrequency of the resonators 74. In a typical example, the resonators 74are of the folded half wavelength type as used in the accelerator at theNational Accelerator Laboratory of Batavia, Illinois. The resonators aretuned to a suitable radio frequency, as of 30 megahertz, and are drivenin the proper phase relation from a 30 megahertz oscillator 75 via phaseshifters 76 and power amplifiers 77.

The power amplifiers 77 are preferably conventional tetrodes providinghigh efficiency, i.e., greater than 90 percent in class C operation withsmall angle of current flow and possibly third harmonic squaring of theplate voltage. Phase-locked magnetron oscillators could also be utilizedas a source of microwave energy for driving the cavities 74, but a lowerfrequency has the further advantage of decreasing debunching effects dueto both velocity spread and space charge effects.

For a finite beam of small diameter in pipe 15, the longitudinal plasmafrequency is proportional to the driving frequency. The plasma frequencyfor a 30 megahertz driving frequency is about 2,000 hertz for a ampere,lOO megavolt beam. The corresponding debunching wavelength is 150kilometers.

lt is desired to maintain the electron bunches for more efficient RFenergy extraction at the receiving location 16. Accordingly, aninductive cavity, i.e., a cavity resonant slightly above the frequencyof the RF driving energy, is placed on the beam 19 every few kilometers,such as 10 These rebunching cavities 78 are excited by the bunched beamentering the cavity and the fields of the cavity interact back on theelectron beam to velocity-modulate the bunched beam in such a manner asto cause a rebunching of the electron. Thus, the electron beam 19 isreceived at the receiving location 16 as a well bunched current densitymodulated beam of high velocity, as of lOO MeV. The beam is bunched atthe frequency of the radio frequency accelerator, such as 30 meghertz.

At the receiving location a plurality of decelerating cavities 79, tunedto the frequency of the radio frequency energy imparted to the beam, aresuccessively coupled to the beam for extracting kinetic energy therefromand converting same to RF energy. The decelerating cavities 79 aresubstantially identical to accelerating cavities 74 and each cavity iscapable of gen erating a relatively high RF voltage thereacross on theorder of 400 kV per cavity.

A rectifier load 81 is connected to each of the cavity resonators 79 forrectifying the RF energy extracted from the beam. The rectified DCenergy is applied to an output coaxial line 82. The output DC energy online 82 is fed to the input of an inverter 24 for producing three phaseoutput power on lines 25-27.

Each of the resonators 79 of the output decelerator section 83 serves toextract kinetic energy from the beam. A sufficient number of outputresonators 79 is provided for extracting the kinetic energy imparted tothe beam by means of the accelerator section 73. After the RF energy hasbeen extracted from the beam, the beam may be collected on the pipe orin a collector 17 coupled to the end of the pipe 15. As in the otherembodiments, an output signal is derived from the inverter which is ameasure of the power demanded by the load. This load demand signal isfed to one input ot the control circuit 28 for controlling the beamcurrent such that the power delivered to the load is equal to the powerdemanded by the load.

The inverter 24 may be replaced by two additional sets of rectifiers 81which may comprise, for example, high power triodes. Each set of trioderectifiers is connected to a respective output bus similar to bus 82.There is one output bus for each phase of a three phase system. Eachoutput bus is connected to a primary winding of a three phase powertransformer. The respective sets of triode rectifiers are sequentiallygated at the AC power frequency, as of 60 Hertz, with 120 phase shiftbetween each of the output power buses.

As an alternative, the gun 12 may be gated at the 60 Hertz powerfrequency and the three sets of output triode rectifiers synchronizedwith the 60 Hertz pulses of the beam.

An advantage to the high velocity electron beam transmission system ofFIG. 16 is that the self magnetic field of the beam almost completelyovercomes the re pulsive space charge forces generated within the beam.

As an alternative to varying the beam current in the system of FIG. 16,for matching the power delivered to the load to the power demanded bythe load, the beam current is maintained constant and the number ofresonators 74 employed for accelerating the beam varied in accordancewith the output power demanded by the load.

Power is tapped off the beam intermediate the transmitting location 14and the receiving location 16 by providing an output resonator 79coupled in wave energy exchanging relation to the RF modulated beam andexcited by the beam. As with the other output resonators 79, the RFpower extracted via the cavity 79 is rectified via rectifier 81 and fedto a second load 80. The load 80 may comprise an inverter for providingthree phase output power or three sets of rectifiers may be employedwhich are sequentially switched into a primary winding of a three phasetransformer for providing inversion of the power to the load.

The intermediate output power tap comprising the resonator 79, rectifier81, and load 80 is also utilized with any of the other Dc transmissionsystems such as 11, 42, or FIG. 9, by pulse modulating the beam at theresonant frequency of the cavity 79 without the necessity of theaccelerating and decelerating RF structures 73 and 83.

Referring now to FlGS. 17-19, a number of circuits are shown forcontrolling the beam of the transmitting end 14 to insure that theelectrons collected by collector 17 strike the collector at nearly zerovelocity so that no large amount of power is dissipated in the collector17 (i.e. the system efficiency will be high). This zero velocitycondition is realized when the cathode potential V,, V,v I R where V, isthe collector potential, I is the electron beam current, and R, is theload resistance presented to the collector 17.

There are two ways of accomplishing this end. First, both V and l,, areadjusted simultaneously so that V V... Secondly the beam current 1,, isadjusted to be equal to V /R by sensing the collector voltage V andsetting the current i, so that V equals V All of the above methods relyupon a comparison circuit for comparing V and V to derive the errorcontrol signal. The comparison circuit comprises an analog summingamplifier or a combination of analog-todigital converters and digitalsumming logic of the type shown in FIG. 19. More particularly, withregard to FIG. 19, the collector voltage V, is fed to a firstanalogto-digital converter 91 to derive a first digital outputproportional to V,.. The cathode potential 1,, is applied to a secondanalog-to-digital converter 92 to derive a second digital outputproportional to V;,. The two digital output are applied to a logicsubtractor 93 for substraction therein to derive the error signal in theform of a digital output which is thence fed to a digital-toanalogconverter 94 to derive an analog control signal (error signal).

The error signal, either analog or digital, which is proportional to thedifference between the cathode potential V, and collector potential Vcontrols the system parameter selected for control.

Referring now to FIG. 17, there is shown a control circuit for matchingthe cathode potential V to the collector potential V In the circuit ofFIG. 17 the cathode potential V is varied to be equal to the collectorpotential V while allowing the beam current to vary with variations inthe cathode potential. The beam current I, will vary as a function ofthe cathode potential V according to the relation: 1,, KV, where K isthe beam perveance.

In the variable voltage cathode power supply 38, the difference signalcoming from the comparison circuitry 28 is used to vary the mechanicalposition of a variable mutual inductance transformer, such as anlnductrol, therein for varying the output potential V,,. As analternative, the error signal derived from the output of the comparisoncircuit 28 is utilized as the input signal to a phase control regulatorincorporated in the variable voltage power supply 38 for varying VReferring now to FIG. 18, there is shown the second method for matchingthe cathode potential V to the collector potential V The differencesignal from the output of the comparison circuit 28 is amplified andapplied to the control electrode 29 in the proper phase to reduce thedifference signal to zero. In this case, the beam perveance K will varyup to some value which is dependent upon the system voltage (aconstant), and the maximum system current. The beam focus system, suchas the quadrupole, is designed to handle such a range of perveance.

In a further variation of the control system of FIG. 18 the peak currentof the beam l is maintained constant while the average current is variedin accordance with the error signal derived from the comparison circuit28. The average current is varied by creating (in a pulse modulator 96)a repetitive rectangular pulse signal applied to the control grid 29.The duty factor of the repetitive pulse is varied by the output of thecomparison circuit 28 in such a manner that the difference between thecollector potential V and the cathode voltage V tends toward zero. Whenthis control variation is used, there must be enough capacitance in thecollector circuit 17 and the repetition frequency of the current pulseis high enough so that the collector voltage V does not follow the rapidvariations of the beam current I,,. The pulsed version of the controlsystem of FIG. 18 imposes the most easily met requirements on the beamfocus system. Also, the method of FIG. 18 (whether or not pulsed) is themost suitable when it is desired to deliver a varying amount of power tothe receiving end 16 at a constant collector voltage such as would existin the typical power system.

What is claimed is:

1. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to a geographically removed receiving location; transmittermeans at the transmitting location for forming, accelerating andprojecting a beam of electrons over an elongated beam path extendingwithin and along said evacuated envelope from the transmitting locationto the receiving location; and

receiver means at the receiving location for converting kinetic energyof the beam to electrical power for application to a power load,comprising, means for decelerating the electrons by an electric fieldcomponent in the direction of their motion and means for collecting thedecelerated electrons as conduction current.

2. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationdisposed remote from the transmitting location:

an elongated evacuated envelope means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitter means for accelerating and projecting a beam of electronsover an elongated beam path ex tending within and along said evacuatedenvelope between the transmitting location and the geographicallyremoved receiving location;

receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load; and

beam focus means disposed along said beam path intermediate thetransmitting and receiving locations for focusing the electron beamwithin said evacuated envelope, said bean focus means comprising magnetmeans for generating a magnetic beam focusing field within the beampath, and magnetic shield means disposed surrounding said magnet meansand said elongated evacuated envelope.

3. The apparatus of claim 2 wherein said magnet means comprises a pluralpole permanent magnet structure.

4. The apparatus of claim 2 wherein said magnet means is a plural polemagnet and comprises a plurality of circumferentially spaced electricalconductors spiraling around the outside of said envelope, and means forenergizing said conductors with current to generate said plural polebeam focusing magnetic field within the beam path.

5. The apparatus of claim 3 wherein said plural pole permanent magnetstructure comprises at least four circumferentially spaced permanentmagnet structures disposed spiraling around the outside of saidelongated evacuated envelope.

6. The apparatus of claim I wherein said receiving means includes anelectron-collecting structure to collect the electrons of the beam,electrical insulator means for electrically insulating said collectorstructure from said elongated evacuated envelope means to allow thepotential of said collector means to be depressed to within 5% of the DCpotential corresponding to the Kinetic energy of electrons of the beam.

7. The apparatus of claim 1 wherein said transmitter means includes aplurality of accelerating electrodes spaced apart along the beam path,insulator means disposed between adjacent electrodes to permit differentbeam accelerating potentials to be applied to different ones of saidaccelerating electrodes. means for applying as ascending sequence ofdifferent DC potentials taken in the direction of beam flow to saidplurality of accelerating electrodes to produce a DC beam acceleratingelectric potential gradient in and along the beam path for acceleratingthe electrons.

8. The apparatus of claim 1 wherein said receiver means includes, beamdecelerating structure comprising a plurality of decelerating electrodesspaced apart along the beam path, insulator means disposed betweenadjacent decelerator electrodes to permit different beam deceleratingpotentials to be established on different ones of said deceleratingelectrodes, means for applying a descending sequence of differentpotentials taken in the direction of beam flow through said plurality ofdecelerating electrodes to produce a beam decelerating electricpotential gradient in and along the beam path for decelerating theelectrons to a beam collecting potential.

9. The apparatus of claim 1 wherein said receiving means includes a pairof beam collector structures for each phase of output current to besupplied to the load, and receiver beam deflector means for sequentiallydefleeting the beam into respective ones of said beam collectorstructures, whereby alternating current is supplied to said load.

10. The apparatus of claim 9 wherein said transmitter means includes apair of electron guns for each phase of alternating current to besupplied to the load at said receiver means of the power transmissionsystem and transmitter beam deflector means at the transmitting locationfor sequentially deflecting the beam current from respective ones ofsaid electron guns into a common beam path within said elongatedevacuated envelope means.

11. The apparatus of claim 10 including, means for synchronizing thebeam deflecting actions of said beam deflector means at both thetransmitting and receiving locations of the power transmission system.

12. The apparatus of claim 10 wherein the power transmission system is athree phase electrical power transmission system having six beam formingelectron guns and six beam collector structures.

13. The apparatus of claim 1 wherein said transmitting means and saidreceiving means includes a pair of electron guns and a pair of beamcollecting structures, respectively, for each phase of alternatingoutput current to be supplied to the load at the receiving location ofthe power transmission system, and means for sequentially directingcurrent from respective ones of said electron guns to respective ones ofsaid beam collecting structures.

14. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationdisposed remote from the transmitting location:

an elongated evacuated envelope means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitting means for accelerating and projecting a beam of electronsover an elongated beam path extending within and along said evacuatedenvelope between the transmitting location and the geographicallyremoved receiving location; receiver means at the receiving location forextracting kinetic energy from said beam and converting same toelectrical power for application to a power load; and

control means responsive to the power demanded by the power load, asconnected to said receiving means, for controlling the beam powertransmitted from the transmitting location to the receiving location inproportion to the power load demanded at the receiving location.

15. The apparatus of claim 14 wherein said control means includes, meansfor deriving a beam collector signal indicaline of the potential drop V,produced by the flow of collected beam current through the power loadconnected to said receiver means, said transmitter means including acathode emitter means for supplying beam current, and means forcontrolling the potential V of said cathode emitter means to a valuewithin at least percent of said collector potential V 16. The apparatusof claim 14 wherein said power transmitter means includes a cathodeemitter means operating a cathode potential V,, for supplying beamcurrent, control electrode means for controlling the value of beamcurrent drawn from said cathode emitter means, and wherein said controlmeans includes, means for deriving a beam collector signal indicative ofthe potential drop V, produced by the flow of collected beam currentthrough the power load connected to said receiver means, and means forcontrolling the potential of said control electrode means forcontrolling the beam current to a value such that the collectorpotential V, is controlled to a value within at least 10 percent of thevalue of the cathode potential V 17. The apparatus of claim 16 whereinsaid means for controlling the potential of said control electrodeincludes means for pulsing the potential applied to said controlelectrode in such a manner that the average beam current is controlledto such a value that the collector potential V is controlled to a valuewithin at least 10 percent of the value of the cathode potential V,,.

18. In an electron beam power transmission system for transmitting powerfrom a transmitting location to a receiving location disposed remotefrom the transmitting location;

an elongated evacuated envelope structure extending from thetransmitting location to the geographically removed receiving location;

transmitter means for accelerating and projecting a beam of electronsinto an elongated beam path extending within and along said evacuatedenvelope between the transmitting location and the receiving location;

receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load;

said beam accelerating means including a radio frequency wave supportivebeam accelerating structure disposed in electromagnetic wave energyexchanging relation with the beam at the transmitting location;

means for exciting said radio frequency accelerating structure forapplying the excited radio frequency electric fields of said structureto the beam path with a substantial component of said radio frequencyfield being directed in the direction of the beam path for bunching andaccelerating the electrons of the beam; and

said receiver means including a radio frequency wave supportivereceiving structure disposed at the receiving location inelectromagnetic wave energy exchanging relation with said beam forexcitation by the accelerated and bunched beam. and rectifier meanscoupled to said radio frequency wave supportive receiving structure forrectifying the radio frequency power extracted from the beam.

19. The apparatus of claim 18 wherein said radio frequency acceleratorstructure includes a plurality of radio frequency resonators. and meansfor phasing the electrical fields of said resonators for acceleratingand bunching the electron beam.

20. The apparatus of claim 18 wherein said means for exciting said radiofrequency accelerating structure includes a class C radio frequencyamplifier means.

21. The apparatus of claim 18 including, a resonant radio frequency wavesupportive electron beam rebunching structure disposed along said beampath in electromagnetic wave energy exchanging relation with the beamfor rebunching the electron bunches of the beam to counteract spacecharge debunching effects within the beam.

22. The apparatus of claim 18 wherein said radio frequency receivingstructure includes a plurality of radio frequency resonators spacedapart along the beam path in radio frequency electromagnetic wave energyexchanging relation with the beam.

23. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to the geographically removed receiving location; transmittermeans for accelerating and projecting electrons into an elongated beampath extending within and along said evacuated envelope means betweenthe transmitting location and the receiving location; receiving means atthe receiving location for extracting kinetic energy from the electronsand for converting same to electrical power for application to a powerload; and

means for pulsing the beam current into a train of pulses each having apulse length of sufficiently short duration to avoid ion neutralizationof the space charge of the beam and successive pulses being separated bya time sufficiently long to permit the ions to diffuse to the envelope,whereby ions formed within the beam path will drain to the walls of saidelongated envelope.

24. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting lo- 65 cation; transmitter means at the transmittinglocation for accelerating and projecting electrons through saidevacuated envelope means along a beam path from the transmittinglocation to the receiving location; receiver means at the receivinglocation for converting the kinetic energy of the beam to electricalpower for application to a power load; and

ion draining electrode means disposed along said beam path in gascommunication therewith for draining and collecting the ions, wherebyions formed within the beam path will be drained to said ion drainingelectrode means.

25. In an electron beam power transmission system for transmittingelectrical power from a transmitting location:

elongated evacuated envelope means extending from 5 the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitter means at the transmitting location for accelerating andprojecting electrons through said evacuated envelope means from thetransmitting location to the receiving location; receiver means at thereceiving location for collecting the electrons and for converting thekinetic energy thereof to electrical power for application to a powerload; and

means disposed intermediate the transmitting location and the receivinglocation for extracting kinetic energy from the beam and for convertingsame to electrical power for application to a second power load.

26. The apparatus of claim 25 wherein said transmitter means includes,means for current density modulating the beam at a radio frequency, andwherein said means for extracting kinetic energy from the beam includesa radio frequency wave supporting structure coupled in electromagneticwave energy exchanging relation to the beam for extracting radiofrequency wave energy therefrom, and rectifier means for rectifying theradio frequency energy extracted from the beam.

27. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitter means for accelerating and projecting electrons into anelongated beam path extending within and along said evacuated envelopemeans between the transmitting location and the receiving location;

receiver means at the receiving location for extracting kinetic energyfrom the beam and for converting same to electrical power forapplication to a power load; and

means for pulsing the duty factor of the beam current for variablycontrolling the average beam power transmitted to the receivinglocation.

28. In an electron beam transmission system for transmitting electricalpower from a transmitting location to a receiving location remote fromthe transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to the geographically removed receiving location;

transmitter means for accelerating and projecting electrons into anelongated beam path extending within said along said evacuated envelopemeans between the transmitting location and the receiving location;

receiver means at the receiving location for extracting kinetic energyfrom the beam and for converting same to electrical power forapplication to a power load; and means coupled in radio frequency waveenergy exchanging relation with the interior of said elongated evacuatedenvelope for coupling to and suppressing modes of radio frequency waveenergy propagation within said envelope.

29. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location:

an electrically conductive pipe means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location; transmitter means at the transmitting locationfor accelerating and projecting electrons over an elongated beam pathextending within and along said pipe from the transmitting location tothe receiving location; receiver means at the receiving location forcollecting the electrons of the beam and for converting the kineticenergy of the beam into electrical cur rent and potential forapplication to a load; and

means for returning the beam current from the receiving location to thetransmitter location via electrical conduction through the walls of saidelectrically conducting pipe means.

30. The apparatus of claim 29 wherein said pipe means is evacuated.

31. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationdisposed remote from the transmitting location:

elongated evacuated envelope structure extending from the transmittinglocation to the receiving lo cation geographically removed from thetransmitting location;

transmitter means for accelerating and projecting a beam of electronsover an elongated beam path extending within and along said evacuatedenvelope between the transmitting location and the receiving location;

receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load;

beam focus means disposed along said beam path intermediate thetransmitting and receiving locations for focusing the electron beamwithin said evacuated envelope, said beam focus means comprising aplural pole magnet means for generating a mag netic beam focusing fieldwithin the beam path; said transmitter means including a cathode emittermeans for emitting electrons to form the beam; and said beam focus meansincluding a main portion and a transition portion. said transitionportion providing a taper in the intensity of the beam focusing magneticfield so as to gradually increase the inten sity of the beam focusmagnetic field from a rela tively low intensity to full intensity in thebeam path as a function of distance in the direction of electron flowfrom said cathode emitter into said main portion of said beam focusmeans. whereby a smooth transition to full beam focusing field intensityis obtained to minimize perturbations of electron beam flow.

32. in an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationdisposed remote from It) the transmitting location:

elongated evacuated envelope means extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitter means for accelerating and projecting a beam of electronsover an elongated beam path extending within and along said evacuatedenvelope between the transmitting location and the receiving location;

receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load; beam focus means disposed along said beam pathintermediate the transmitting and receiving locations for focusing saidelectron beam within said evacuated envelope, said beam focus meanscomprising a plural pole magnet means for generating a magnetic beamfocusing field within the beam path;

said transmitting means including a cathode emitter means for emittingelectrons to form the beam; and

said beam focus means including a main portion disposed intermediate thetransmitting and receiving locations and a transition portion at thetransmitting location. said transition portion comprising a multi-poleastigmatic magnetic lens means for receiving the electron beam from saidcathode emitter means and for focusing the received electron beam intosaid main portion of said beam focus means with electron trajectoriesmatching the entrance electron trajectory requirements of said mainportion of said beam focus magnet means, whereby a smooth transition ofthe electron flow is obtained from said cathode emitter means into themain portion of said beam focus means to minimize undesiredmagnetic-beam-focus caused perturbations of the electron beam flow.

33. In a magnetic cable for use in an electron beam power transmissionsystem for transmitting electrical power from a transmitting location toa geographically removed receiving location:

an electrically conductive pipe for transmission of an electron beamtherethrough between the transmitting and receiving locations;

plural pole magnet means for generating a magnetic beam focusing fieldwithin said pipe. said magnet means being disposed externally of saidpipe; and

magnetic shield means disposed surrounding said magnet means and saidpipe for shielding the interior of said pipe from spurious externalmagnetic fields and for providing a magnetic return path for themagnetic flux generated by said magnet means.

34. The apparatus of claim 33 wherein said magnet means comprises aplural pole permanent magnet structure.

35. The apparatus of claim 33 wherein said magnet means comprises atleast four circumferentially spaced electrical conductors spiralingaround the outside of said pipe.

36. The apparatus of claim 33 wherein said magnet means comprises atleast four circumferentially spaced permanent magnet structures disposedspiraling around the outside of said pipe.

37. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationdisposed remote from the transmitting location:

elongated evacuated envelope structure extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location;

transmitter means for accelerating and projecting a beam of electronsover an elongated beam path ex tending within and along said evacuatedenvelope teraction with the beam.

1. In an electron beam power transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location: elongated evacuated envelopemeans extending from the transmitting location to a geographicallyremoved receiving location; transmitter means at the transmittinglocation for forming, accelerating and projecting a beam of electronsover an elongated beam path extending within and along said evacuatedenvelope from the transmitting location to the receiving location; andreceiver means at the receiving location for converting kinetic energyof the beam to electrical power for application to a power load,comprising, means for decelerating the electrons by an electric fieldcomponent in the direction of their motion and means for collecting thedecelerated electrons as conduction current.
 2. In an electron beampower transmission system for transmitting electrical power from atransmitting location to a receiving location disposed remote from thetransmitting location: an elongated evacuated envelope means extendingfrom the transmitting location to the receiving location geographicallyremoved from the transmitting location; transmitter means foraccelerating and projecting a beam of electrons over an elongated beampath extending within and along said evacuated envelope between thetransmitting location and the geographically removed receiving location;receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load; and beam focus means disposed along said beam pathintermediate the transmitting and receiving locations for focusing theelectron beam within said evacuated envelope, said bean focus meanscomprising magnet means for generating a magnetic beam focusing fieldwithin the beam path, and magnetic shield means disposed surroundingsaid magnet means and said elongated evacuated envelope.
 3. Theapparatus of claim 2 wherein said magnet means comprises a plural polepermanent magnet structure.
 4. The apparatus of claim 2 wherein saidmagnet means is a plural pole magnet and comprises a plurality ofcircumferentially spaced electrical conductors spiraling around theoutside of said envelope, and means for energizing said conductors withcurrent to generate said plural pole beam focusing magnetic field withinthe beam path.
 5. The apparatus of claim 3 wherein said plural polepermanent magnet structure comprises at least four circumferentiallyspaced permanent magnet structures disposed spiraling around the outsideof said elongated evacuated envelope.
 6. The apparatus of claim 1wherein said receiving means includes an electron-collecting structureto collect the electrons of the beam, electrical insulator means forelectrically insulating said collector structure from said elongatedevacuated envelope means to allow the potential of said collector meansto be depressed to within 5% of the DC potential corresponding to theKinetic energy of electrons of the beam.
 7. The apparatus of claim 1wherein said transmitter means includes a plurality of acceleratingelectrodes spaced apart along the beam path, insulator means disposedbetween adjacent electrodes to permit different beam acceleratingpotentials to be applied to different ones of said acceleratingelectrodes, means for applying as ascending sequence of different DCpotentials taken in the direction of beam flow to said plurality ofaccelerating electrodes to produce a DC beam accelerating electricpotential gradient in and along the beam path for accelerating theelectrons.
 8. The apparatus of claim 1 wherein said receiver meansincludes, beam decelerating structure comprising a plurality ofdecelerating electrodes spaced apart along the beam path, insulatormeans disposed between adjacent decelerator electrodes to permitdifferent beam decelerating potentials to be established on differentones of said decelerating electrodes, means for applying a descendingsequence of different potentials taken in the direction of beam flowthrough said plurality of decelerating electrodes to produce a beamdecelerating electric potential gradient in and along the beam path fordecelerating the electrons to a beam collecting potential.
 9. Theapparatus of claim 1 wherein said receiving means includes a pair ofbeam collector structures for each phase of output current to besupplied to the load, and receiver beam deflector means for sequentiallydeflecting the beam into respective ones of said beam collectorstructures, whereby alternating current is supplied to said load. 10.The apparatus of claim 9 wherein said transmitter means includes a pairof electron guns for each phase of alternating current to be supplied tothe load at said receiver means of the power transmission system andtransmitter beam deflector means at the transmitting location forsequentially deflecting the beam current from respective ones of saidelectron guns into a common beam path within said elongated evacuatedenvelope means.
 11. The apparatus of claim 10 including, means forsynchronizing the beam deflecting actions of said beam deflector meansat both the transmitting and receiving locations of the powertransmission system.
 12. The apparatus of claim 10 wherein the powertransmission system is a three phase electrical power transmissionsystem having six beam forming electron guns and six beam collectorstructures.
 13. The apparatus of claim 1 wherein said transmitting meansand said receiving means includes a pair of electron guns and a pair ofbeam collecting structures, respectively, for each phase of alternatingoutput current to be supplied to the load at the receiving location ofthe power transmission system, and means for sequentially directingcurrent from respective ones of said electron guns to respective ones ofsaid beam collecting structures.
 14. In an electron beam powertransmission system for transmitting electrical power from atransmitting location to a receiving location disposed remote from thetransmitting location: an elongated evacuated envelope means extendingfrom the transmitting location to the receiving location geographicallyremoved from the transmitting location; transmitting means foraccelerating and projecting a beam of electrons over an elongated beampath extending within and along said evacuated envelope between thetransmitting location and the geographically removed receiving location;receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load; and control means responsive to the power demanded bythe power load, as connected to said receiving means, for controllingthe beam power transmitted from the transmitting location to thereceiving location in proportion to the power load demanded at thereceiving location.
 15. The apparatus of claim 14 wherein said controlmeans includes, means for deriving a beam collector signal indicaline ofthe potential drop Vc produced by the flow of collected beam currentthrough the power load connected to said receiver means, saidtransmitter means including a cathode emitter means for supplying beamcurrent, and means for controlling the potential Vk of said cathodeemitter means to a value within at least 10 percent of said collectorpotential Vc.
 16. The apparatus of claim 14 wherein said powertransmitter means includes a cathode emitter means operating a cathodepotential Vk for supplying beam current, control electrode means forcontrolling the value of beam current drawn from said cathode emittermeans, and wherein said control means includes, means for deriving abeam collector signal indicative of the potential drop Vc produced bythe flow of collected beam current through the power load connected tosaid receiver means, and means for controlling the potential of saidcontrol electrode means for controlling the beam current to a value suchthat the collector potential Vc is controlled to a value within at least10 percent of the value of the cathode potential Vk.
 17. The apparatusof claim 16 wherein said means for controlling the potential of saidcontrol electrode includes means for pulsing the potential applied tosaid control electrode in such a manner that the average beam current iscontrolled to such a value that the collector potential Vc is controlledto a value within at least 10 percent of the value of the cathodepotential Vk.
 18. In an electron beam power transmission system fortransmitting power from a transmitting location to a receiving locationdisposed remote from the transmitting location; an elongated evacuatedenvelope structure extending from the transmitting location to thegeographically removed receiving location; transmitter means foraccelerating and projecting a beam of electrons into an elongated beampath extending within and along said evacuated envelope between thetransmitting location and the receiving location; receiver means at thereceiving location for extracting kinetic energy from said beam andconverting same to electrical power for application to a power load;said beam accelerating means including a radio frequency wave supportivebeam accelerating structure disposed in electromagnetic wave energyexchanging relation with the beam at the transmitting location; meansfor exciting said radio frequency accelerating structure for applyingthe excited radio frequency electric fields of said structure to thebeam path with a substantial component of said radio frequency fieldbeing directed in the direction of the beam path for bunching andaccelerating the electrons of the beam; and said receiver meansincluding a radio frequency wave supportive receiving structure disposedat the receiVing location in electromagnetic wave energy exchangingrelation with said beam for excitation by the accelerated and bunchedbeam, and rectifier means coupled to said radio frequency wavesupportive receiving structure for rectifying the radio frequency powerextracted from the beam.
 19. The apparatus of claim 18 wherein saidradio frequency accelerator structure includes a plurality of radiofrequency resonators, and means for phasing the electrical fields ofsaid resonators for accelerating and bunching the electron beam.
 20. Theapparatus of claim 18 wherein said means for exciting said radiofrequency accelerating structure includes a class C radio frequencyamplifier means.
 21. The apparatus of claim 18 including, a resonantradio frequency wave supportive electron beam rebunching structuredisposed along said beam path in electromagnetic wave energy exchangingrelation with the beam for rebunching the electron bunches of the beamto counteract space charge debunching effects within the beam.
 22. Theapparatus of claim 18 wherein said radio frequency receiving structureincludes a plurality of radio frequency resonators spaced apart alongthe beam path in radio frequency electromagnetic wave energy exchangingrelation with the beam.
 23. In an electron beam power transmissionsystem for transmitting electrical power from a transmitting location toa receiving location remote from the transmitting location: elongatedevacuated envelope means extending from the transmitting location to thegeographically removed receiving location; transmitter means foraccelerating and projecting electrons into an elongated beam pathextending within and along said evacuated envelope means between thetransmitting location and the receiving location; receiving means at thereceiving location for extracting kinetic energy from the electrons andfor converting same to electrical power for application to a power load;and means for pulsing the beam current into a train of pulses eachhaving a pulse length of sufficiently short duration to avoid ionneutralization of the space charge of the beam and successive pulsesbeing separated by a time sufficiently long to permit the ions todiffuse to the envelope, whereby ions formed within the beam path willdrain to the walls of said elongated envelope.
 24. In an electron beampower transmission system for transmitting electrical power from atransmitting location to a receiving location remote from thetransmitting location: elongated evacuated envelope means extending fromthe transmitting location to the receiving location geographicallyremoved from the transmitting location; transmitter means at thetransmitting location for accelerating and projecting electrons throughsaid evacuated envelope means along a beam path from the transmittinglocation to the receiving location; receiver means at the receivinglocation for converting the kinetic energy of the beam to electricalpower for application to a power load; and ion draining electrode meansdisposed along said beam path in gas communication therewith fordraining and collecting the ions, whereby ions formed within the beampath will be drained to said ion draining electrode means.
 25. In anelectron beam power transmission system for transmitting electricalpower from a transmitting location: elongated evacuated envelope meansextending from the transmitting location to the receiving locationgeographically removed from the transmitting location; transmitter meansat the transmitting location for accelerating and projecting electronsthrough said evacuated envelope means from the transmitting location tothe receiving location; receiver means at the receiving location forcollecting the electrons and for converting the kinetic energy thereofto electrical power for application to a power load; and means disposedintermediate the transmitting location and the receiving location forextracting kinetic eNergy from the beam and for converting same toelectrical power for application to a second power load.
 26. Theapparatus of claim 25 wherein said transmitter means includes, means forcurrent density modulating the beam at a radio frequency, and whereinsaid means for extracting kinetic energy from the beam includes a radiofrequency wave supporting structure coupled in electromagnetic waveenergy exchanging relation to the beam for extracting radio frequencywave energy therefrom, and rectifier means for rectifying the radiofrequency energy extracted from the beam.
 27. In an electron beam powertransmission system for transmitting electrical power from atransmitting location to a receiving location remote from thetransmitting location: elongated evacuated envelope means extending fromthe transmitting location to the receiving location geographicallyremoved from the transmitting location; transmitter means foraccelerating and projecting electrons into an elongated beam pathextending within and along said evacuated envelope means between thetransmitting location and the receiving location; receiver means at thereceiving location for extracting kinetic energy from the beam and forconverting same to electrical power for application to a power load; andmeans for pulsing the duty factor of the beam current for variablycontrolling the average beam power transmitted to the receivinglocation.
 28. In an electron beam transmission system for transmittingelectrical power from a transmitting location to a receiving locationremote from the transmitting location: elongated evacuated envelopemeans extending from the transmitting location to the geographicallyremoved receiving location; transmitter means for accelerating andprojecting electrons into an elongated beam path extending within saidalong said evacuated envelope means between the transmitting locationand the receiving location; receiver means at the receiving location forextracting kinetic energy from the beam and for converting same toelectrical power for application to a power load; and means coupled inradio frequency wave energy exchanging relation with the interior ofsaid elongated evacuated envelope for coupling to and suppressing modesof radio frequency wave energy propagation within said envelope.
 29. Inan electron beam power transmission system for transmitting electricalpower from a transmitting location to a receiving location remote fromthe transmitting location: an electrically conductive pipe meansextending from the transmitting location to the receiving locationgeographically removed from the transmitting location; transmitter meansat the transmitting location for accelerating and projecting electronsover an elongated beam path extending within and along said pipe fromthe transmitting location to the receiving location; receiver means atthe receiving location for collecting the electrons of the beam and forconverting the kinetic energy of the beam into electrical current andpotential for application to a load; and means for returning the beamcurrent from the receiving location to the transmitter location viaelectrical conduction through the walls of said electrically conductingpipe means.
 30. The apparatus of claim 29 wherein said pipe means isevacuated.
 31. In an electron beam power transmission system fortransmitting electrical power from a transmitting location to areceiving location disposed remote from the transmitting location:elongated evacuated envelope structure extending from the transmittinglocation to the receiving location geographically removed from thetransmitting location; transmitter means for accelerating and projectinga beam of electrons over an elongated beam path extending within andalong said evacuated envelope between the transmitting location and thereceiving location; receiver means at the receiving location forextracting kinetic energy from said beaM and converting same toelectrical power for application to a power load; beam focus meansdisposed along said beam path intermediate the transmitting andreceiving locations for focusing the electron beam within said evacuatedenvelope, said beam focus means comprising a plural pole magnet meansfor generating a magnetic beam focusing field within the beam path; saidtransmitter means including a cathode emitter means for emittingelectrons to form the beam; and said beam focus means including a mainportion and a transition portion, said transition portion providing ataper in the intensity of the beam focusing magnetic field so as togradually increase the intensity of the beam focus magnetic field from arelatively low intensity to full intensity in the beam path as afunction of distance in the direction of electron flow from said cathodeemitter into said main portion of said beam focus means, whereby asmooth transition to full beam focusing field intensity is obtained tominimize perturbations of electron beam flow.
 32. In an electron beampower transmission system for transmitting electrical power from atransmitting location to a receiving location disposed remote from thetransmitting location: elongated evacuated envelope means extending fromthe transmitting location to the receiving location geographicallyremoved from the transmitting location; transmitter means foraccelerating and projecting a beam of electrons over an elongated beampath extending within and along said evacuated envelope between thetransmitting location and the receiving location; receiver means at thereceiving location for extracting kinetic energy from said beam andconverting same to electrical power for application to a power load;beam focus means disposed along said beam path intermediate thetransmitting and receiving locations for focusing said electron beamwithin said evacuated envelope, said beam focus means comprising aplural pole magnet means for generating a magnetic beam focusing fieldwithin the beam path; said transmitting means including a cathodeemitter means for emitting electrons to form the beam; and said beamfocus means including a main portion disposed intermediate thetransmitting and receiving locations and a transition portion at thetransmitting location, said transition portion comprising a multi-poleastigmatic magnetic lens means for receiving the electron beam from saidcathode emitter means and for focusing the received electron beam intosaid main portion of said beam focus means with electron trajectoriesmatching the entrance electron trajectory requirements of said mainportion of said beam focus magnet means, whereby a smooth transition ofthe electron flow is obtained from said cathode emitter means into themain portion of said beam focus means to minimize undesiredmagnetic-beam-focus caused perturbations of the electron beam flow. 33.In a magnetic cable for use in an electron beam power transmissionsystem for transmitting electrical power from a transmitting location toa geographically removed receiving location: an electrically conductivepipe for transmission of an electron beam therethrough between thetransmitting and receiving locations; plural pole magnet means forgenerating a magnetic beam focusing field within said pipe, said magnetmeans being disposed externally of said pipe; and magnetic shield meansdisposed surrounding said magnet means and said pipe for shielding theinterior of said pipe from spurious external magnetic fields and forproviding a magnetic return path for the magnetic flux generated by saidmagnet means.
 34. The apparatus of claim 33 wherein said magnet meanscomprises a plural pole permanent magnet structure.
 35. The apparatus ofclaim 33 wherein said magnet means comprises at least fourcircumferentially spaced electrical conductors spiraling around theoutside of said pipe.
 36. The apparatus of claim 33 wherein said magnetmeans compRises at least four circumferentially spaced permanent magnetstructures disposed spiraling around the outside of said pipe.
 37. In anelectron beam power transmission system for transmitting electricalpower from a transmitting location to a receiving location disposedremote from the transmitting location: elongated evacuated envelopestructure extending from the transmitting location to the receivinglocation geographically removed from the transmitting location;transmitter means for accelerating and projecting a beam of electronsover an elongated beam path extending within and along said evacuatedenvelope between the transmitting location and the receiving location;receiver means at the receiving location for extracting kinetic energyfrom said beam and converting same to electrical power for applicationto a power load; beam focus means disposed along said beam pathintermediate the transmitting and receiving locations for focusing theelectron beam within said evacuated envelope, said beam focus meanscomprising a periodic beam focus magnet structure, and wherein theperiod of said periodic beam focus magnet structure varies randomlyalong the beam path to avoid undesired radio frequency wave interactionwith the beam.